December 29, 1911] 



SCIENCE 



923 



extensive three-dimensional world. The 

 former problem was in principle solved by 

 Wheatstone, and its perfection in securing an 

 orthostereoscopic effect — apart from conve- 

 nience and refinement — follows upon the an- 

 alyses and elimination of the incidental and 

 unintentional deviations between the optical 

 system of the photographic reproduction, and 

 that of the original visual experience. Inven- 

 tion has been fertile, especially in devices for 

 presenting to the eyes the two divergent 

 views, leading to such diverse pieces of view- 

 ing apparatus as the reflecting stereoscope of 

 Wheatstone, the refracting one of Brewster, 

 the lenticular of Helmholtz, the complemen- 

 tary chromatic effect of Rollman-d' Almeida, 

 the Ives parallax stereogram, the unilateral 

 reflecting stereoscope of Pigeon, and in 

 another direction, to the invention of the 

 Verant lenses; in yet another, to the devices 

 for stereoscopic projection, and again to the 

 study of pseudostereoscopy. The enlarge- 

 ment and precision of stereoscopic vision has 

 led to the stereotelemeter, in which the pro- 

 jection of a scale incorporated in the optical 

 system of the instrument (by engraved lines 

 on the ' objective, or equivalent device) over 

 the distant landscape gives accurate stereo- 

 scopic judgments at a telescopic range. Con- 

 versely the stereo-comparator provides the 

 means of restoring to space-relations of the 

 third dimension, the minute transverse devia- 

 tions of the two divergent representations re- 

 sulting from any given real (or calculated) 

 base line. From this, in turn, other problems 

 diverge, such as that of constructing an 

 equally precise photographic stereo-camera, 

 and again of restoring from the stereograms 

 thus resulting, the actual object- — say, a 

 statue — in its three dimensional reality. 

 No less accurately than a phonographic disc 

 preserves a voice for posterity may a solid 

 reproduction of our actual bodily self in 

 length, breadth, thickness of build and fea- 

 ture, be embodied on the twin record of a 

 true stereoscopic print. Finally, of applica- 

 tions of stereoscopic principles there are 

 many and varied examples, from the detec- 

 tion of forgeries to that of the variability of 



stars, or examination of microscopic speci- 

 mens. 



Pullfrich's article is devoted not to the de- 

 scription or analytic aspects of the problems 

 of which these several inventions form the 

 solutions, but to the clear and concise state- 

 ment of the physical (and mathematical) as- 

 pects of the constructions involved, with due 

 reference to the functional service sought. 

 For this specific purpose, as well as for a gen- 

 eral survey of the recent advances in stereo- 

 scopy, the pamphlet may be unreservedly 

 recommended. Joseph Jastrow 



De Fabricatie van Suiker uii Suiherriet op 

 lava. By H. C. Prinsen Geerligs. Am- 

 sterdam, J. H. De Bussy. 1911. Second 

 edition. Pp. xxiv -(- 500 + ^^s. 

 Desire to keep pace with the rapid advances 

 which the art of sugar-making is constantly 

 experiencing has induced Prinsen Geerligs, the 

 well-known Dutch sugar-expert and author, to 

 prepare this new edition of his book, which 

 was originally published in 1907. 



The work is divided into three sections. 

 The first of these is given over to a considera- 

 tion of the raw material and discusses the oc- 

 currence and distribution of the various con- 

 stituents of the sugar-cane — sucrose, dextrose, 

 lasvulose, invert-sugar, fiber, the pectins, or- 

 ganic acids, cane-wax, coloring matters, nitro- 

 genous bodies and mineral matters. 



The second section is concerned with the 

 technology of sugar-making. Attention is 

 first given to the extraction of the juice from 

 the cane and in this connection there are con- 

 sidered, sugar-mills, processes of diffusion, the 

 treatment of bagasse and determination of its 

 fuel-value. Then follows an exhaustive dis- 

 cussion of various processes of defecation and 

 carbonatation, having for their object the 

 clarifying of the crude cane-juice, and a de- 

 tailed review of various reagents employed for 

 the purpose. 



Under the caption " Concentration of the 

 Juice," the author deals with the preliminary 

 concentration of sugar solutions, vacuum-pans 

 and their accessories, and the working up of 

 by-products. 



